13 April 2009

Tui are back! Returning Banks Peninsula's lost birds

The lowlands of Canterbury, New Zealand, have gone through about as complete an ecological transformation as can be imagined. Before Polynesian settlers arrived, around 800 years ago, the Canterbury lowlands were cloaked with diverse native forest. By the time European settlers arrived, 650 years later, most of this forest had been burned off. It has since been almost entirely replaced with farms and towns, dominated by foreign species imported by settlers and their descendants. Banks Peninsula botanist Hugh Wilson has likened the arrival of people here to a harpoon hitting a whale.

With the almost complete loss of forest and the arrival of foreign pests, lowland Canterbury lost a lot of its bird species. Lincoln ornithologist, Kerry-Jayne Wilson, collated the native terrestrial birds that we've lost from lowland Canterbury's Banks Peninsula in her 2004 book, The Flight of the Huia. Between Polynesian settlement and European settlement, we lost at least eight species, including several moa species and brown kiwi. Since European settlement, we lost a further 15 species, including the New Zealand quail (Coturnix novaezelandiae) from which Quail Island in Lyttelton harbour takes it name. For some of these species, like the quail, all we have left are specimens in museums. They are lost forever, unless future molecular biology labs can one day rebuild them from their DNA. Others survive elsewhere in New Zealand, like kaka, buff weka, and yellow-crowned and red-crowned parakeets. As native forest regrows on Banks Peninsula, these lost birds can be returned.

And so it was, on 9 April, 2009, on a wet stormy day in a forest clearing low down in Hinewai Reserve, that 30 tui (Prosthemadera novaeseelandiae) were released back onto Banks Peninsula. Kerry-Jayne had not included tui in her list of lost birds, since solitary birds have been sighted occasionally on the Peninsula. However, ecologically they were certainly among the lost, as there hadn't been a breeding population of the birds here since at least the 1980s.

Hinewai Reserve (see map) and many other Banks Peninsula forest reserves and covenants have regrown and matured substantially over the past 30 years. An ecological assessment in 2007 by Hugh Wilson concluded that there was now sufficient food year-round to support a tui population. Banks Peninsula's original tui populations may have missed the development of Hinewai Reserve, founded in 1987 to restore a large area of native forest to the south-eastern corner of Banks Peninsula. Now they have an opportunity to explore it. The 30 released birds are being radio-tracked and carefully watched by Lincoln University behavioural ecologist, Laura Molles, and her team. She hopes that the released tui will found a new breeding population, and will be the first of many successful reintroductions of our lost birds.

It is a long way from Banks Peninsula to the nearest healthy tui population. The nearest populations in Canterbury are about 130 km away in the Lake Sumner area, separated from the Peninsula by the deforested pastoral expanse of the Canterbury Plains. The Lake Sumner population was not considered healthy enough to spare birds. Indeed, the nearest healthy tui population living in a forest type comparable to Banks Peninsula was on Maud Island in the Marlborough Sounds, a predator-free reserve managed by the Department of Conservation 320 km to the north.

In the week prior to the Banks Peninsula release, a team of experienced bird handlers, led by Wayne Beggs of the Department of Conservation, caught 30 Maud Island tui, a mix of male and female adults and juveniles. They were housed in temporary aviaries before being placed in cardboard cat boxes, two to a box, and flown by helicopter directly to Hinewai Reserve. If these 30 birds stick around, they will be joined by a further 50 birds from Maud Island next year to ensure a genetically diverse founding population.

Reintroductions are not easy. The often complex logistics, community and inter-agency organisation and consents combined to require several years of planning for the tui release. A large team of volunteers and staff from a menagerie of Canterbury agencies and Ngai Tahu have worked hard over the past several years to bring about the tui release. Then there is an enormous amount of ecological uncertainty involved in what happens next. Once the birds are let go, how do you encourage them to stay put? Their natural instinct after a long and stressful journey is often to scatter and head for home. One famous male tomtit promptly flew home, a journey of over 60 km, after being part of a group of 32 birds moved in 2004 from the Hunua Ranges in southern Auckland to Tiritiri Matangi Island in the Hauraki Gulf. In February of 1993, 15 South Island robins, another species lost from Banks Peninsula, were released in Hinewai Reserve. The last sighting was of one bird on 2 July 1993. Where they went, nobody knows.

Laura Molles together with colleagues at the University of Waikato has pioneered the use of acoustic anchoring as a technique to encourage released forest birds to stay where they're released. Her idea is that if the released birds hear the songs of other birds from their home population, they will conclude that the release site is good habitat (and contains potential mates) and they'll stay to explore rather than dispersing. Acoustic anchoring has been associated with several successful kokako reintroductions (also called translocations) in the North Island and is being used with the Banks Peninsula tui release and a release of North Island Robins back into the Coromandel Peninsula.

For the Banks Peninsula tui release, the team have also placed well-stocked bird feeders in forest clearings around the release site. These feeders are of the same design that the birds got used to using on Maud Island prior to the release. Everyone hopes that this, combined with hearing the songs of Maud Island tui every morning, will be sufficient encouragement for the released birds to stay and explore Hinewai.

So far, the results are promising. Three days after the release, the birds were still in the release area. They had discovered several fruiting kahikatea trees and were feasting and singing. Singing! This was the first tui song heard in Hinewai in a very long time. It's as good a start as anyone could have hoped for.

The big test will be what they do in the spring, when they want to breed. Will the adults try to head home to their Maud Island territories, or will they be content to set up territories in Hinewai? Will adult and juvenile birds differ? Lots of Cantabrians hope they'll all choose to stay.

Over the past decades, Hinewai Reserve has seen the spreading of a native forest cloak back over a corner of lowland Canterbury. Now, tui song at Hinewai heralds a return of the lost birds. With that song comes a great hope that some of the past centuries' ecological transformation of lowland Canterbury can be undone to make room for wild native nature.

Ecology & Evolution @ Lincoln

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